This is a revised application for renewal of a research project aiming to determine how motor experience during early life influences the development of the cortical motor representations and corticospinal connections. The first aim is to study the relationships between the normal morphological and functional development of CS axon terminal arbors. The second aim is to determine the roles of motor experience and neural activity during early life in shaping the functional and morphological development of corticospinal terminal arbors and of cortical motor representations. The third aim is to determine the effects of impaired limb use or cortical activity blockade during development on kinematics and dynamic control of skilled movements. By understanding experiential factors influencing early development of the corticospinal system and skilled movements, the investigators hope to devise more targeted interventional and rehabilitation strategies.